The present invention relates to local area networks and, more particularly, to local area network topologies based on serial intelligent cells.
Bus Topology
Most prior art local area networks (LAN) use a bus topology as shown by example in FIG. 1. A communication medium 102 is based on two conductors (usually twisted pair or coaxial cable), to which data terminal equipment (DTE) units 104, 106, 108, 110, and 112 are connected, via respective network adapters 114, 116, 118, 120, and 122. A network adapter can be stand-alone or housed within the respective DTE.
This prior art bus topology suffers from the following drawbacks:
1. From the point of view of data communication, the medium can vary significantly from one installation to another, and hence proper adaptation to the medium cannot always be obtained.
2. The bus topology is not optimal for communication, and hence:
a) the maximum length of the medium is limited;
b) the maximum number of units which may be connected to the bus is limited;
c) complex circuitry is involved in the transceiver in the network adapter;
d) the data rate is limited.
3. Terminators are usually required at the ends of the medium, thus complicating the installation.
4. Only one DTE can transmit at any given time on the bus, and all other are restricted to be listeners.
5. Complex arbitration techniques are needed to determine which DTE is able to transmit on the bus.
6. In case of short circuit in the bus, the whole bus malfunctions, and it is hard to locate the short circuit.
7. Addresses should be associated independently with any network adapter, and this is difficult to attain with bus topology.
Star Topology
A number of prior art network devices and interconnections summarized below utilize star topology.
The multiplexer is a common item of equipment used in communication, both for local area networks and wide-area networks (WAN""s). It is used in order to provide access to a data communications backbone, or in order to allow sharing of bandwidth between multiple stations. As shown in FIG. 2, one side of a multiplexer 202 is usually connected to a single high data rate connection 204 (xe2x80x9chighwayxe2x80x9d), but several such connections can also be used. The other side of multiplexer 202 has multiple low data rate connections 206, 208, 210, 212, and 214. The ellipsis indicates that additional connections can be made. Each low data rate connection uses art of the bandwidth offered by the high data rate connection. These low data rate connections can be of the same type or different types, and can have different or identical data rates. The multiplexing technique most commonly used is time-domain multiplexing (TDM). However, frequency-domain multiplexing (FDM) is also used.
A popular multiplexer in use is the voice multiplexer, shown in FIG. 3. A pulse-code modulation (PCM) bus 304 handling 2.048 megabits per second, containing 30 channels of 64 kilobits per second is connected to one side of a PABX/PBX 302, and up to 30 telephone interfaces 308, 312, and 316 are connected to the other side via connections 306, 310, and 314. The ellipsis . . . indicates that additional connections can be made. In this configuration, each channel in the PCM bus can be switched or be permanently dedicated to a specific telephone line. An example of such system is disclosed in U.S. Pat. No. 3,924,077 to Blakeslee.
Similarly a small private branch exchange (PABX/PBX), as shown in FIG. 4, is widely used (usually in an office or business environment) where several outside lines 403, 404, and 405 are connected to one side of a PABX/PBX 402, and multiple telephones 408, 412, and 416 are connected to the other side via lines 406, 410, and 414, respectively. The ellipsis . . . indicates that additional connections can be made. The PABX/PBX connects an outside line to a requesting or requested telephone, and allows connection between telephones in the premises.
In the configurations described above, star topology is used in order to connect to the units to the multiplexer, which functions as the network hub. The disadvantages of star topology include the following:
1. A connection between each unit and the network hub is required, and the wiring required for this connection can involve a lengthy run. Thus, when adding new unit, an additional, possibly lengthy, connection between the new unit and the network hub must be added.
2. No fault protection is provided: Any short circuit or open circuit will disrupt service to the affected units.
3. The multiplexer can impose extensive space and power requirements.
Computer Interfaces
Various interface standards have been established in order to allow interoperability between the PC (personal computer) or workstation and its various connected elements. These standards usually relate to both mechanical and electrical interfaces, and include industry standard architecture (ISA), extended industry standard architecture (EISA), Personal Computer Memory Card Industry Association (PCMCIA), intelligent drive electronics (IDE), small computer system interface (SCSI), and others. Each added hardware unit usually utilizes a specific software driver for interoperability with the specific platform. These protocols are applicable to small distances only, and allow units to be housed within or nearby the PC or workstation enclosures. For example, equipping a PC for video capture could involve a plug-in ISA card housed within the PC on the motherboard, a video camera connected to the card, and a software driver. This configuration does not allow remote video monitoring.
Relevant Prior Art
The use of the same wire pair or pairs for both power and data communication is well known, and is widely used in telecommunications, from xe2x80x9cPlain Old Telephone Servicexe2x80x9d (xe2x80x9cPOTSxe2x80x9d) to Integrated Services Digital Network (ISDN) and broadband services in the local-loop including other Digital Subscriber Line (xDSL) technologies. Such a concept is described, for example, in U.S. Pat. No. 4,825,349 to Marcel, describing using two pairs for such a scheme. A DC-to-DC converter for such DC feeding is described, for example, in U.S. Pat. No. 4,507,721 to Yamano et al.
The concept of power line communication (PLC) is also widely known. However, in most cases the connection is similar to a LAN environment, in which a single transmitter occupies the entire medium. Examples of such techniques include X-10 and the consumer electronics bus (CEBus, described in the EIA-600 standard). Much of this technology uses complex spread-spectrum techniques in order to accommodate problematic media (characterized by high amounts of noise and interference). Even with such improved technologies, however, the data rate obtained is relatively low.
Prior art in this field includes U.S. Pat. No. 5,684,826 to Ratner, U.S. Pat. No. 5,491,463 to Sargeant et.al U.S. Pat. No. 5,504,454 to Daggett et al., U.S. Pat. No. 5,351,272 to Abraham, U.S. Pat. No. 5,404,127 to Lee et al., U.S. Pat. No. 5,065,133 to Howard, U.S. Pat. No. 5,581,801 to Spriester et al., U.S. Pat. No. 4,772,870 to Reyes, and U.S. Pat. No. 4,782,322 to Lechner et al. Other patents can be found in U.S. Class 340/310 (sub-classes A/R and others) and International Class H04M 11/04.
The concept of using existing telephone wiring also for data communication is first disclosed in U.S. Pat. No. 5,010,399 to Goodman et al., where video signals superimposed over the telephone signals are used. However, the scheme used is of the bus type and has the drawbacks of that topology. Similarly, the idea of data transmission over a public switched telephone network (PSTN) using the higher frequency band is widely used in the xDSL systems, as is disclosed in U.S. Pat. No. 5,247,347 to Litteral et al. The patent discloses an asymmetric digital subscriber line (ADSL) system. However, only a single point-to-point transmission is described over the local-loop, and existing in-house wiring is not discussed, and thus this prior art does not disclose how to configure a full multipoint network. Multiplexing xDSL data and the POTS/ISDN data uses FDM principles, based on the fact that the POTS/ISDN services occupy the lower portion of the spectrum, allowing for the xDSL system to use the higher bandwidth.
A home bus network using dedicated wiring is disclosed in U.S. Pat. No. 4,896,349 to Kubo et al., and a home automation network based on a power line controller (PLC) is disclosed in U.S. Pat. No. 5,579,221 to Mun. U.S. Pat. No. 4,714,912 to Roberts et al. is the first to suggest communicating data over power lines not in bus topology but as xe2x80x98break-and-insertxe2x80x99. However, only single conductor is used, and the receivers are all connected again using a bus topology.
In addition, U.S. patent application Ser. No. 08/734,921, Israel Patent Application No. 119454, and PCT Patent Application No. PCT/IL97/00195 of the present inventor disclose a distributed serial control system of line-powered modules in a network topology for sensing and control. These documents, however, do not disclose a local area network for data communications.
The prior art documents mentioned above are representative examples in the field. Certain applications are covered by more than one issued patent.
There is thus a widely recognized need for, and it would be highly advantageous to have, a means of implementing a local area network for data communications which does not suffer from the limitations inherent in the current methods. This goal is met by the present invention.
The present invention is of a local area network for data communication, sensing, and control based on serially connected modules referred to as xe2x80x9cserial intelligent cellsxe2x80x9d (SIC""s). An example of a local area network of such devices according to the present invention is illustrated in FIG. 7, to which reference is now briefly made. In this example, SIC""s 700, 702, 704, 706, and 708 are connected by one or more conducting wire pairs (such as a twisted pair 710). This allows chaining, such as SIC 700 to SIC 702 to SIC 704. However, SIC 700, SIC 706, and SIC 708, located at the ends are equipped with single connection. SIC 704 is equipped with three connections, and even more connections are possible. A SIC may be interfaced to one or more DTE""s, as illustrated by a DTE 714 interfaced to SIC 700 and by DTE""s 716 and 718 interfaced to SIC 704. SIC""s need not have an interface, however, as is illustrated by SIC 706 and SIC 702. SIC 702, though, serves as a repeater, connecting SIC 700 and SIC 704. It is to be noted that the networks according to the present invention utilize electrically-conducting media to interconnect the SIC""s. Each electrically-conducting medium connects exactly two SIC""s into a communicating pair of SIC""s which communicate bidirectionally and independently of other communicating pairs in the local area network. Electrically-conducting media are media which transmit signals by conducting electrical current or by propagating electrical potential from one point to another. Electrically-conducting media include, but are not limited to wires, twisted pair, and coaxial cable. But electrically-conducting media do not include media such as fiber optic lines, waveguides, microwave, radio, and infrared communication media.
As noted above, SIC""s in a communicating pair communicate bidirectionally. For example, SIC 704 can initiate communication (as a sender) to SIC 702 (as a receiver), but SIC 704 can just as well initiate simultaneous communication (as a sender) to SIC 700 (as a receiver). Bidirectional communication can take place simultaneously, and herein is taken to be equivalent to xe2x80x9cfull duplexxe2x80x9d communication. In addition, as noted above, the communication between the SIC""s of a communicating pair is independent of the communication between the SIC""s of any other communicating pair, in that these communications neither preclude nor affect one another in any way. Furthermore, every communication between SIC""s is a xe2x80x9cpoint-to-point communicationxe2x80x9d, which term herein denotes a communication that takes place between exactly one sender and exactly one receiver. This is in contrast to a bus-based communication, in which there are many (potential) receivers and many (potential) senders. Consequently, in the topology according to the present invention, there is automatically a termination in the physical layer at each end of a connection (a SIC), both simplifying the installation and insuring more reliable communication.
The topology according to the present invention is superior to the prior art bus topology in the following ways:
1. There is no physical limit to the number of SIC""s which may be installed in the network, and hence no physical limit to the number of DTE""s in the network.
2. Point-to-point communication allows higher data rates over greater distances.
3. Point-to-point communication requires less complex circuitry than bus circuitry.
4. Several SIC""s can transmit and receive simultaneously. For example, SIC 700 can communicate with SIC 702 while SIC 704 communicates simultaneously with SIC 706.
5. There is no need for arbitration, allowing more efficient utilization of the network. Furthermore, priorities can be assigned to each SIC or, alternatively, to each specific message to allow the data routing to take care of priorities.
6. Addresses may be assigned by the network.
7. In the case of failure of any conductor or SIC, the network can sense the fault immediately, and the specific location of the fault (up to the specific SIC pair) is easily obtained.
Therefore, according to the present invention there is provided a local area network for data communication, sensing, and control including a plurality of serial intelligent cells interconnected exclusively by electrically-conducting media into at least one communicating pair, wherein: (a) each of the electrically-conducting media interconnects no more than two of the serial intelligent cells; (b) each of the communicating pair includes one of the electrically-conducting media and exactly two of the serial intelligent cells; (c) each of the communicating pair engages in a communication exclusively over the electrically-conducting media; and (d) each of the communicating pair engages in the communication bidirectionally and independently of the communication of any other of the communicating pair.